1. Field of the Invention
This invention relates generally to, AO deflectors, and more particularly to a low loss crystal as a large aperture AO deflector.
2. Description of the Related Art
An Acousto-Optic traveling lens scanner utilizes a frequency modulated acoustic wave packet to focus a diffracted laser beam. The focus power is determined by the rate of change of acousto-optic diffraction angles across the wave packet. The acoustic wave packet is typically short relative to the full optical aperture of the Acousto-optic device. The focused spot scans as the acoustic packet travels across the device aperture at a speed determined by the velocity of the acoustic wave packet. Therefore the optical scan velocity is equivalent to the acoustic packet propagation velocity. In this mode of operation, much higher scanning data rates can be achieved than with other Acousto-Optic or mechanical scanning methods (VanderLugt and Bardos).
An Acousto-Optic traveling lens system comprises a laser producing a collimated laser beam, a beam expander, an Acousto-Optic bragg cell with a piezoelectric transducer (the traveling lens device), a chirped pulse RF frequency synthesizer, Cylindrical scan optics. In the preferred embodiment, there is an orthogonal axis scan mechanism, either steering the laser beam or mechanically translating the substrate with respect to the scanning mechanism. That way, the focal spot scans across a two-dimensional surface, the “optical scan plane”.
This system may also include an Acousto-Optic tracker to increase the optical efficiency, as disclosed in U.S. Pat. No. 3,851,951 hereafter the (“'951 Patent”).
In the '951 Patent, a preliminary Bragg deflector is used so that not the whole cell with the traveling lens needs to be illuminated, but only the lens itself. This improves light efficiency from laser to focused spot. As the wave packet reaches the end of the aperture, the tracker cell needs to redirect the light to the next pulse at the transducer end of the traveling lens device. The faster this flyback time, the less dead-time the system has. Using Sapphire for the tracker Bragg cell makes this fast because the speed of sound is high.